Discovery of large gas and gas-condensate fields in Jurassic and Cretaceous rocks of the Barents-Kara platform marked the opening of a new oil-gas province on the Arctic Shelf of Russia. The largest of these discoveries in the Barents Sea are on the Shtokmanov-Lunin mega-saddle, which is a complex feature of 87,000 sq km with a closure of 500 m on the Jurassic-Cretaceous rocks. This mega-saddle lies between the South Barents and North Barents depressions. It consists of east-west-trending uplifted and subsided features: Shtokmanov-Ledov, Ludlov, and Lunin saddles and Severo-Shtokmanov and Yuzhno-Lunin downwarps. Growth of the mega-saddle began in the Middle Jurassic and continued in subsequent time.
The structure of the Shtokmanov-Lunin mega-saddle has now been found to be more complicated and its history of development more lengthy than previously thought. Also, structures of this type appear to be present extensively on the Barents-Kara platform and are very favorable for large hydrocarbon deposits.
The earliest stage in formation of the sedimentary cover of the Barents Shelf appears to have begun in the Late Proterozoic. It includes Riphean-Lower Paleozoic clastics and also Middle and Upper Paleozoic carbonate-clastic deposits. At the base of this complex is acoustical basement, and at its top everywhere on the shelf is a regional discordance of Early Permian age. This discordance marks change from predominant carbonate deposition to clastic deposition and is a marker seismic reflector.
The map of thickness of the sediments between the base and top of this complex indicates with some approximation the paleo-relief of the base at the time when deposition was complete. Recognized in the paleo-relief of this acountical basement is a system of large structural features. The largest of these is the Barents-Yamal mega-downwarp, which extends from the South Barents depression through Novaya Zemlya and continues with reduced thickness into the south of the Kara Shelf and possibly finally into the structures of the Yamal region (Urengoy-Koltogor graben). In the west of the Barents Shelf this ancient structure may correspond with the Nordkap downwarp.
To the north of the Barents-Yamal mega-downwarp is a newly recognized paleo-structure of the same orientation - the Barents-Kara belt of highs. Extending from west to east for a distance of more than 1500 km, this belt combines several large highs - Persius high, Admiralty swell and part of Novaya Zemlya, Rusanov paleo-swell on the Kara Shelf, and the northern end of Yamalia. The saddle between the Persius high and the Admiralty swell corresponds in modern structural plan with the Shtokmanov-Lunin mega-saddle.
The Barents-Kara belt of highs played a definite role in deposition of the sedimentary cover of the region. To the north of this belt are several paleo-swells and downwarps. The time of formation of these structures corresponds with Baykalian tectonism.
Taken from Gramberg, Suprunenko, and Shipel'kevich, 2001. Digested in
Petroleum Geology, vol. 36, 2002, in preparation, three paleo-structural
maps, two cross sections, and one seismic section. You are encouraged
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